The Keithley 3721 Dual 1x20 Multiplexer Card offers two independent banks of 1x20 two-pole multiplexers that are ideal for general purpose switching, including temperature measurements. The two banks can automatically be connected to the Series 3700 mainframe backplane and optional DMM through the analog backplane connection relays. This connection allows the mainframe to reconfigure the 3721 as a single 1x40 two-pole multiplexer or to enable card-to-card expansion for even larger configurations.

The 3721 provides a number of other features. In addition to the 40 channels, two fused channels are supplied for current measurements. Also, the 3721 includes dedicated inputs that enable 40 channels of four-wire common side ohms measurements.

The 3721 uses two 50-pin male D-sub connectors for signal connections.